Using 2001 data from the EPA AQS database,
the daily co-occurrence PM2.5 and NO2 over a 24-h period was
characterized. There were 200 sites where PM2.5 and NO2 monitors
were co-located. A daily co-occurrence of NO2 and PM2.5 was subjectively
defined as when an hourly average NO2 concentration greater than
or equal to 0.05 ppm and a PM2.5 24-h concentration equal to
or greater than 40 ug/m3 occurred over the same 24-h period.
Figure 1 illustrates the daily co-occurrence patterns observed.
Using 2001 data from the AQS database, the daily co-occurrence
of PM2.5 and NO2 was infrequent.

Figure 1. The co-occurrence pattern for
NO2 and PM2.5 using 2001 data from AQS.

The information on this web site can be
referenced as Lefohn, A.S. (2006). Co-occurrence of Nitrogen
Dioxide and Daily PM2.5. http://www.asl-associates.com/co_occurrence_NO2_PM25.htm.